The present invention relates to the field of optical transmission of data, and relates specifically to metrics for the evaluation of transmission losses in optically amplified fiber optic cables.
The telecommunications industry is experiencing an increased demand for bandwidth due to the convergence of Internet traffic and more traditional types of voice and data traffic. To meet this increased demand, industry is moving toward the use of fiber optic cables to be able facilitate handling such convergent traffic. Fiber optic cable is especially beneficial in long-distance cabling because it is lightweight compared to the more traditional copper cable. Fiber is also desirable because it is inexpensive, compact, reliable, and efficient. Fiber optic transmission systems provide inherent high power throughput.
A typical fiber optic cable is an amalgamation of different fiber types. Typically, one particular type of fiber will dominate the length of a span of fiber, while other types of fiber will constitute lesser lengths of the entire span. Each type of fiber has a distinct set of properties. When different fiber types are combined within a span, the properties of each of these fiber types must be considered when attempting to achieve a desired set of properties for the entire span of fiber.
In particular, if a large segment of foreign fiber has been incorporated into a fiber span, it is important to identify and confirm specifications of the loss properties of that foreign length of cable.
Prior art in-system span loss measurements have generally been limited to the gathering of mean power measurements at both a transmit amplifier output and at a receive amplifier input, the amplifiers being at either end of the span being measured. The power at the transmit amplifier is subtracted from the power at the receive amplifier to obtain a mean loss value for the fiber span. However, in certain applications, such as Raman amplification, the measurement of a mean span loss value is insufficient. In such cases, a complete mapping of the fiber loss profile across a desired frequency spectrum may be desired.
One manner of obtaining information regarding the loss profile of a fiber is to identify the fiber type. Specific knowledge of accurate specifications relating to the loss properties of each type of fiber within a span would permit estimation of the loss profile of a fiber span comprising different fiber types. However, such accurate specifications are not always available. In fact, fiber optic system administrators or manufacturers may inadvertently provide or obtain outdated or incorrect specifications relating to the properties and lengths of the fiber types comprised within a fiber optic span.
Consequently, prior art methods of fiber identification are unreliable to the extent that they depend on the questionable accuracy of the theoretical data upon which such a fiber identification is based. Therefore, a fiber optic system administrator may be required to estimate the actual information related to fiber types within a span, which may result in greater losses and inefficient signal transmission over the entire span.
It is an object of the present invention to provide a method and system for automatically identifying a fiber type in an optically amplified fiber span.
According to an aspect of the invention, there is provided a method of automatically identifying a fiber type in an optically amplified fiber optic span, said span having connected thereto a transmit amplifier, and a receive amplifier, said method comprising the steps of: obtaining a spectral power profile near each of said transmit amplifier and said receive amplifier; determining a score for said fiber span based on a spectral loss profile for said fiber span; and comparing said score with known identification scores in a lookup table in order to make a positive determination of the fiber type for the fiber span if the measured score matches a score in the table within a given tolerance.
According to another aspect of the invention, there is provided a method of automatically identifying a fiber type in an optically amplified fiber optic span, said span having connected thereto a transmit amplifier, and a receive amplifier, said method comprising the steps of: obtaining a first spectral profile near said receive amplifier; applying a Raman pump laser to said system; obtaining a second spectral profile near said receive amplifier after said step of applying the Raman pump laser; determining a score for said fiber span based on a Raman gain profile for said fiber span; and comparing said score with known identification scores in a lookup table in order to make a positive determination of the fiber type for the fiber span if the measured score matches a score in the table within a given tolerance.
According to a further aspect of the invention, there is provided a fiber type identification system for automatically identifying a fiber type in an optically amplifiable fiber optic span comprising: one or more optical spectrum analyzers for measuring a spectral profile near one or more amplifiers attached to said fiber optic span; a lookup table of known identification scores for each of a plurality of fiber types; means for calculating a score based on said profile measurements; and means for comparing said score to the known identification scores in the lookup table in conjunction with a given tolerance in order to identify the fiber type.
The present invention permits the identification of a fiber type in an active network, as opposed to relying on theoretical information that was obtained during passive testing of the individual network components. According to the present invention, it is also possible to identify whether a hybrid splice exists within a particular fiber span. Furthermore, the present invention permits mapping of the fiber types for each span within a fiber link. Consequently, an auto mapping of a network is possible, based on each of these link mappings.